lein.bat fixes

Hi,

I've tried to make some improvements to the Windows .bat files.  Particularly to enable a leiningen installer that I'm working on at:
<https://bitbucket.org/djpowell/leiningen-win-installer>

The first commit adds back support for curl and wget for windows if powershell isn't available.  It seems that powershell is not installed by default before Windows 7.  I'm working on an installer for lein, and it is much easier for the installer to ensure that a curl.exe is available, than to ensure that powershell is installed.

The second commit simplifies the handling of double quotes in LEIN_JAVA_CMD and JAVA_CMD by partially reverting <https://github.com/technomancy/leiningen/pull/778>.
Prior to this commit, setting LEIN_JAVA_CMD to paths containing parenthesis would cause lein to fail.  This is an issue, because 32-bit JDKs on Win-64 are installed in locations such as: "C:\Program Files (x86)\Java\jdk1.7.0_06".

The new commit supports paths with and without surrounding double quotes, with and without spaces, and with and without parentheses.  It doesn't attempt to sanitize mangled paths, but I don't see that as important.